Electron discharge device



Oct. 19, 1937. H. w. WEINHART ELECTRON DISCHARGE DEVICE Filed Dec. 27,1933 2 Sheets-Sheet l //V|/ENTOR fin. WE/NHART MAM 7M A TTORNE V Oct.19, 1937. H. w. WEINHART ELECTRON DISCHARGE DEVICE Filed Dec. 27, 1933 2Sheets-Sheet 2 FIG. 5A

T v, M NH WW W m H M B m m /\I Patented Oct. 19,1937

UNITED STATES ELECTRON DISCHARGE DEVICE Howard W. Welnhart, Elizabeth,N. 3., asaignor to Bell Telephone laboratories, Incorporated, New York,N. Y., a corporation of New York Application December 27, 1933, SerialNo. 704,101

8 Claims.

This invention relates to electron discharge devices and moreparticularly to a device of the type in which a cathode ray beam isprojected toward a fluorescent screen on one end of the device.

In an evacuated cathode ray device in which it is desired to focuselectrons projected from an vessel evacuated to a high degree in whichgas ionization is wholly eliminated so that all the electrons emitted bythe emission source reach the fluorescent screen in a small and welldefined spot.

Another object of the invention is to control the focusing of the beamby a system of electron optical lenses to insure concentration of thebeam of electrons.

These and other objects may be attained in accordance with thisinvention in an enclosing vessel which is evacuated to a very highdegree and in which no gas is present to form an ionized sheath toaffect the focusing of the cathode ray beam. The vessel is provided witha stem at one end from which the main electrodes are supported and witha fluorescent screen at the other end which becomes luminous at the spotstruck by the electrons so that deflections of the beam, due toimpressed forces, can be seen or 5 photographed. The electrode structurefor producing the cathode ray beam comprises an electron source oremitting cathode supported by the stem in the axis of the vessel andsurrounded by a tubular shield having a closure at one end provided witha central aperture. An enclosing chamber is superimposed on the tubularshield and overlaps it to avoid stray paths for the electrons to thewall of the vessel. This chamber supports a tubular anode in the axis ofthe vessel and two baflle plates spaced apart in the chamber between theanode and tubular shield form a trapping enclosure for any strayelectrons which are not projected axially through the aperture in thebafile plate adjacent the anode. The anode is of sufficient length tocompel the electrons to follow an axial path in the form of a pencil orbeam. When the beam emerges from the end of the anode it iselectrostatically controlled by a long tubular member which has one endoverlapping the anode. When the beam emerges from the end of the longtubular member it is further acted upon by a second electrostatic memberthat may be in the form of a conductive coating on the wall of theglass, or a second metallic cylinder overlapping the end of the firstelectrostatic mem- 5 her. After the beam passes through the electricfields created by the electrostatic members it may be deflected by pairsof oppositely disposed ele ments and projected on the fluorescent screenformed on the end of the vessel. 10

In order to maintain the intensity of the beam after deflection and toovercome charging of the vessel wall and also to eliminate reflectionwhich might deleteriously affect the indication of the tracing on thescreen, the remaining portion of 16 the wall of the vessel is coatedwith a non-metallic coating, such as colloidal graphite.

A method of forming the coating on the vessel and the necessaryapparatus therefor is disclosed and claimed in my copending application,Serial 20 No. 740,877, filed August 22, 1934, and comprises a coatingreceptacle involving a reservoir containing "Aquadag or colloidalgraphite which is connected to an enclosing vessel by a suitablepassageway and air under pressure forces the graph- 25 ite material torise into the vessel to a proper level. The air trapped above theincoming liquid is removed through an outlet pipe and when the desiredamount of coating material is injected into the vessel the air supply isremoved from the res- 30 ervoir and applied to the outlet pipe. Thepressure of air entering the vessel forces the coating liquid to flowback into the reservoir and when all the excess liquid is removed auniform coating of colloidal graphite adheres to the wall of the vessel.5 The coating is dried and baked by heating to form a hard and adherentcoating on the vessel. This method facilitates the application of thecoating and insures a uniform layer of material on the glass wall.Furthermore, the boundary of the 40 coating on the glass wall adjacentthe screen is uniformly spaced from the screen so that thecoating doesnot mask the fluorescent screen material.

Another feature of the invention is the elimi- 45 nation of straydischarges on the wall of the vessel. This is due to the overlappingarrangement of the electrodes so that no electrons can escape toward thewall, to build up electric fields which cause spreading of the beam ofrays. 50

Another feature relates to the arrangement of the electrodes so that thebeam emanating from the electron source is focussed by a system ofternary electron optical lenses which is produced in the vicinity of theshield and trapping chamber and the ends of the anode and electrostaticmember. The potentials applied to these elements set up electric fieldswhich serve to focus the electron stream in the same manner as physicaloptical lenses focus a beam of light. Further-'- more, the field presentat the adjacent ends of the electrostatic members functions as acombination of two lenses to correct distortion in the same sense thattwo optical lenses are used to correct for spherical aberration.

A more detailed understanding of the invention may be obtained from thefollowing description and drawings:

Fig. 1 shows in cross-section one embodiment of a device made inaccordance with this invention and illustrates the detailed arrangementof the various elements;

Fig. 2 illustrates another embodiment of the invention in the form ofunitary assemblies of the electrodes which may be inserted in a vesselsimilar to that shown in Fig. 1;

Fig. 3 shows in cross-section the detailed structure of the electronemitting cathode;

Fig. 4 illustrates one embodiment of the apparatus for performing theoperations for applying a coating on the vessel in accordance with amethod of this invention; and

Figs. 5 and 5A show another embodiment of the invention in which theelectrodes are arranged in two units which cooperate to project acathode stream to a large screen on the: end of the device.

Referring to Fig. 1, the discharge device in one aspect of thisinvention, is embodied in an elongated enclosing vessel |ll having aninwardly pro-- jecting stem terminating in a press I2 in which theleading-in wires for some of the electrodes are embedded. This vesselhas a long tubular portion I3, an outwardly tapered portion 4 forming anextension of the tubular portion and a dome-shaped window portion I5. Afluorescent coating or screen I 6 is deposited on the inner 1 surface ofthe window portion. A highly efficient fluorescent coating may be formedon the window portion of the vessel in accordance with the disclosure inU. S. Patent 1,603,284, granted October 19, 1926 to J. B. Johnson. Thescreen I6 becomes fluorescent upon impact by an electron beam and showsa figure on the screen when the beam is influenced or deflected bycircuit under test which gives an indication of the type of curve orvariation desired to be shown. The electron beam emanates from a primarysource, such as an equipotential cathode or emitter ll, shown moreclearly in Fig. 3. This cathode comprises a metallic thimble 8 having anemissive coating l9 on the closed end of thermionically activesubstances, such as barium and strontium oxides. Within the thimble isan insulating plug 20 having twin bores through which a heater element2| extends. Between the'end of the plug 20 and the dome of the thimbleI8 is a cavity 22 in which the heater element is looped as shown at 23.The terminations of the heater element 2| are twisted together at 24, toprevent a ripple from being introduced into the cathode beam whenalternating current is employed as the energizing source for the heaterelement. The heater element 2| is connected totwo leading-in wires 25and 26 extending from the press l2, and the thimble I8 is connected toand supported by a conductor 21. The cathode I1 is arranged in the axisof the vessel so that a beam of electrons emanating therefrom isprojected to the axis of the fiuorescent screen on the other end of thevessel l0.

The cathode I1 is surrounded by a tubular screen or shield 28, ofnon-magnetic material, such as aluminum, which is supported from thepress |2 by a short wire 29 and a leading-in wire 30. The top of theshield 28 is closed by a disc 3| having a central aperture substantiallyin alignment with the end of the cathode ll. The disc 3| is attached tothe shield 28 and together with the shield form an enclosure for thecathode IT. The enclosure around the cathode facilitates theconcentration of the emission of electrons from the cathode since thetubular shield 28 prevents any electrons emitted from the cathode fromleaving the confined space within the shield except through theaperture, and "also controls the number of electrons permitted to passthrough the aperture 3|, by applying a suitable potential to theleading-in wire 30, and therefore may be used as a modulating electrodeor trigger control electrode. It, furthermore, conserves the heatgenerated by the cathode.

An anode 32 is arranged in the axis of the vessel in alignment with theaperture in the modulating disc 3| and may be in the form of a tubularmember. The tubular anode 32 is preferably of non-magnetic material,such as aluminum and is rigidly held in position by a chamber whichextends beyond the modulating disc 3|. This chamber has a cup-shapedform and consists of a disc 33 having a central aperture through whichthe anode 32 extends, so that the anode may be afiixed to the disc bysoldering or welding it the inner surface of the disc, and a cylindricalmetallic shield or member 34 of similar material which extendsdownwardly from the disc 33 to a point well beyond the inner end of theshield 28 so that the modulating disc 3| is wholly within the boundaryof the metallic member 34 and the shield 28 is reentrant with respect tothe member 34. The anode 32 and the cup-shaped enclosure comprising thedisc 33 and the cylindrical shield 34 are supported from outwardlyextending wires which are held in supporting members, such as glass IOds35 and 36, which extend from the stem in parallel relation outside therange of the electrodes.

A trapping chamber 31 may be formed intermediate the modulating disc 3|and the anode 32 by two parallel spaced discs 38 and 39, in the form ofbafiie plates with central apertures which are arranged in thecylindrical member 34 and are secured to the walls thereof to form anenclosure to entrap any electrons that are not axially projected fromthe aperture in the primary modulating disc 3|. In order to draw theelectrons from the emission source or cathode I! it is necessary toapply a positive potential to the anode structure. For this purpose aleading-in wire 40, projecting through the side of the cylindricalportion |3 of the vessel, is connected to the anode structure adjacentthe supporting wire attached to the support 35 and the member 34. Thepositive potential applied to the trapping chamber and anode 32 causesan electric field to extend within the scope of the discs 38 and 39 andthereby produce, in effect, a primary electron lens for focussing thebeam of electrons. an electric field extends into the end of the anodeaway from the disc 33 and therefore produces a second electron opticallens through which the beam of cathode rays is projected. In effect, thesecond lens is similar to the first lens, but due to its spacialrelation with respect to the emission source, the beamof cathode rays isconcentrated into a fine pencil of electrons.

' electrostatic electrode 4|.

An elongated electrostatic focusslng member or electrode 4|, in the formof a metallic cylinder 01' non-magnetic material, such as aluminum, issupported in axial alignment with the preceding electrodes bysupportwires extending toward the support rods 35 and 36. This membershould be preferably several times the length of the anode and have adiameter substantially the same as the length of the anode. Furthermore,the end nearest the anode should overlap the anode so that the end ofthe anode is reentrant with respect to the A higher positive potentialis applied to this electrode through a leading-in wire 42 which extendsfrom the cylindrical portion of the vessel and is connected to theelectrostatic electrode 4| by a support wire extending to the supportrod 36. The potential applied to this electrode produces the electricfield which extends into the end of the anode 32 and forms the secondelectron optical lens for focussing the beam of cathode rays projectedtoward the screen at the other end of the vessel. An additional electricfield is produced at the end of this electrode due to the potentialapplied to the conductive coating on the wall of the vesselwhich will bedescribed hereinafter. This field forms a third electron optical lens toconcentrate and focus the stream of electrons and also functions as acorrectional lens similar to an optical lens for the correction ofspherical aberration. The electrostatic focussing produced by the member4| insures concentration of the beam of rays which is projectedtherethrough and the length thereof is closely related to the dimensionsof the anode 32. As an example, the anode 32 may be a tube having aninternal diameter of I; of an inch and a length of inch, while theinside diameter of the Iocussing tubular member 4| may be inch and thelength thereof 3%; inches.

The three-lens system in accordance with this invention insures anoptimum concentration of the cathode beam of electrons which isprojected along the axis of the vessel toward the screen. Furthermore,the overlapping'assembly of the various electrodes insures that none ofthe electrons in the beam can be diverted to the glass wall of thevessel and there build up-electric fields which might influence the beamof cathode rays being projected along the axis of the vessel. It is wellknown that if the glass assumes a negative electric charge electrons inthe beam will be repelled, and consequently such charges on the glasswall will seriously affect the concentration of the electron beamemanating from the cathode. Since the cathode is completely shielded bythe cylinder 28 and only the aperture in the modulating disc 3| permitsa projection of cathode rays and the'area in the vicinity of this discis completely shielded by the depending edge of the shield 34, it isevident that no electrons can escape from the beam toward the wall ofthe vessel. In the same manner the travel of the beam through thetrapping chamber is completely shielded by the cylindrical wall of theshield 34 and when the beam enters the anode 32 it is completelyshielded by the tubular construction of this electrode. Similarly, thepath of the beam is protected along the, whole length of theelectrostatic electrode 4|, due to its cylindrical form.

and the end of the anode is protected because of its reentrantarrangement with respect to electrostatic member 4|. It will thereforebe seen that along the whole path of the beam it is completely shieldedfrom the wall of the vessel so 1 that no electric charges can build upon the wall to influence the cathode beam.

After the beam is projected from the end of the electrostatic focusslngmember 4| it must still travel a considerable distance to the screen ISon the end of the vessel and in order to prevent electric charges frombuilding up on the wall portion between the electrode 4| and the screen,this wall is provided with a non-metallic coating or layer 43, ofcolloidal graphite, commercially known as Aquadag. It will be noted thatthe coating extends beyond the edge of the electrostatic member 4! sothat the end of the member 4| is reentrant with respect to the coating43. This prevents any charges spreading to the wall of the vessel in thehorizontal plane of the end of the member 4!. The graphite coating onthe wall of the vessel prevents the building up of electric charges orfields on the glass wall which might influence the beam of raysprojected to the screen IS. A leading-in wire 44 is sealed in the wallof the vessel adjacent the coating 43 and is connected thereto to applya still higher potential to the coating so that the graphite material inthe coating forms a conductor for establishing a focussing field at theend of the cylinder 4| for the beam of rays projected toward the screen.

In view of the fact that the conductive coating 43 should not ordinarilyflow over the surface of the fluorescent screen l6 it is evident thatconsiderable care must be employed in forming the coating on the innersurface of the vessel wall. An eflicient apparatus for producing thiscoating in the vessel is shown in Fig. 4 in which the vessel I0 isprovided with a removable plug 45 having an inlet tube or connection 46which extends into the vessel ill a slight distance beyond the innersurface of the plug 45. An elongated outlet tube 47 extends through theplug 45 and terminates within the vessel ill at a point slightly beyondthe line to which the coating is desired. The inlet connection 46 is anelongated U-shaped tube which is connected to a reservoir 48 providedwith a valve 49 between the reservoir and the inlet tube 46. A similarvalve 50 is inserted in the mouth of the reservoir and normally is in aclosed condition except when it is desired to replenish the colloidalgraphite material 5| within the reservoir. Adjacent the valve 50 andabove the level of the colloidal graphite coating material Si is atubular projection 52 to which may be connected any source of pressure,such as air.

The method of coating the inner wall of the vessel I 0 consists inopening the valve 49 and applying air pressure to the tube 52 to injectair into the reservoir 48 whereby the coating material is forced intothe vessel It) through the inlet connection 46. The pressure of air ismaintained constant until the level of the coating liquid reaches thelevel of the dotted line 53 in the vessel It). During the filling of thevessel ID with the colloidal material all of the imprisoned air in thevessel displaced by the liquid is ejected through the outlet pipe 41 andwhen the level of the coating material reaches the line 53 the airpressure is removed from the out of the end of the vessel II]. It is tobe understood that in practice the U-shaped tube is mounted in such aposition that the end projecting into the vessel I0 is approximately atthe same height as the level of liquid in the reservoir 48 and that thevessel I0 is above the elevation of the reservoir 48. After the coatingoperation is completed the vessel Ill is dried in an oven and baked toform a hard and adherent coating on the inner wall of the vessel. Thismethodthe glass and the coating such as might be pres-- ent if ametallic coating is applied to the vessel.

While the beam of cathode rays emanating from the cathode is completelycontrolled electrostatically to insure a concentrated beam of electronsand the production of a bright and intense spot on the fluorescentscreen, this spot being of very small diameter, for instance, onemillimeter, it is evident that this beam may be deflected, in any wellknown manner, to cause the indication of the deflection to be reproducedon the fluorescent screen. For instance, the beam may be deflectedelectrostatically by two pairs of oppositely disposed plates such asplates 55 and 56 supported by leading-in wires 51 and 58, respectively,which are sealed through the side wall of the vessel III. A similarplate 59 is shown above the plates 55 and 56 and this plate togetherwith a similar parallel plate, not shown, is arranged at right angles tothe plates 55 and 58 and provided with suitable terminals and supportsthrough the side wall of the vessel. The vessel I0 is highly evacuatedby well known pumping equipment to such a degree that no gas ionizationoccurs in the vessel to influence the focussing of the beam of electronsor enter into the discharge from the emission source. The vessel ishermetically sealed at 63. after the evacuation is completed.

In the device shown in Fig. 1 the anode structure and the electrostaticelement are shown supported from glass standards and the deflectingplates are supported from wires extending through the wall of thevessel. It is evident that this invention may also be embodied in astructure in which the leading-in wires are contained in the stem of thevessel so that all the electrodes may be mounted as a unit on the stemand the unit inserted in the vessel without the need of any otherconnections through the wall of the vessel. Such a structure is shown inFig. 2 in which a stem I having a press l2 surrounding leading-in wires25 and 25 for the heater element 24 and a leading-in wire 21 for theemission source or cathode IT. The cathode is surrounded by acylindrical shield 28 attached to the press by wire 28 and leading-inwire 38. The shield 28 is provided with amodulating disc 3| similar tothe disc shown in Fig. 1. A pair of collars BI and 62 embrace the stemII and carry support rods 53 and 64 which are attached to the shieldmember 34 in which the trapping plates 38 and 39 are situated. The topof the shield 34 is closed by the disc 33 which has a central aperturefor the reception of the tubular anode 32. Surrounding the periphery ofthe disc 33 is an insulating ring or collar 65 having an overhangingedge extending beyond the edge of the disc 33 to readily position theinsulator with respect to the rest of the electrode structure.The'insulating collar may be secured in position by cement 66 whichfills the space between the wall of the shield 34 and the edge of theinsulating collar 65. The insulating collar supports two standards orrods 81 and 58 which are connected to the elongated focussing member 4|.The member 4| is provided at its upper edge with an outwardly projectingflange 69 which forms a base for an insulating ring 10 secured to theflange 58 by cement 'II. The ring 18 carries a short cylindricalmetallic member 12 which is provided with a conductor I3 extending tothe stem. This member and the potential applied to it forms the fleldfor focussing the electron stream at the end of the electrostaticfocussing member 4|. The short cylinder 12 carries an insulating collar14 in which are positioned supports 15 and 18 for the paralleldeflecting plates 11 and I8 and also other supports for the second pairof deflecting plates, only one of which is shown at 19 and connected toa support 88 extending into the insulating ring 14.

anode assembly and this leading-in wire is embedded in a seal betweenthe stem flare and the vessel wall in a manner well known in the art. Aleading-in wire 82 embedded in a seal oppositely disposed with respectto the leading-in wire 8| extends through an insulating glass tubing 83and is connected to the support 88 so that a suitable potential may beimpressed on the electrostatic focussing member 4|. Suitable leading-inwires 84 and 85 extend through the press l2 and are located in aninsulating tubing 86 and separately connected to the supports 15 and 88of the deflecting plates 11 and 19, respectively. On the opposite end ofthe press leadingin wires 81 and 88 extend through an insulating tube 89and the conductor 81 is connected to the support wire 16 of the plate18. It is understood that the conductor 88 is connected to the otherdeflecting plate which is arranged parallel to the plate I8 shown inFig. 2. This arrangement forms a compact and unitary assembly in whichall the electrodes are rigidly held in axial relation so that the beamof rays emanating from the cathode is maintained in the axis of thevarious electrodes.

The device shown in Figs. 5 and 5A is a large embodiment of theinvention in which the stream of electrons is projected for .a distanceof about 3 feet and the diameter of the fluorescent screen isapproximately 15 inches. It is evident that in order for the beam totravel this distance it must be focussed accurately to maintain theintensity of the beam when it reaches the screen. The device consists ofa vessel having a cylindrical portion I8 connected to an outwardlytapered portion .H which continues up to the domeshaped window portionIS on which the screen I5 is deposited. The cylindrical portion of thevessel III is provided with a reentrant tubular portion 88 which is openat its inner end and provided with an outwardly extending long tubularportion 8|. The outer end of the long tubular portion 8| is providedwith a reentrant stem 92 which terminates in a press portion 93. Thepress supports leading-in wires 94 and 95 for the inand a conductorattached to the cathode is sealed in the press at 91. A hollowcup-shaped der I05 or highly purified material, such as magnesiumsilicate or isolantite". The insulating cylinder forms a support for theanode assembly and the elongated focussing electrode and rigidlymaintains the space relation of these elements.

-' The anode structure consists of a. single piece of metal having a cupportion I06 and a shorttu- .bular portion I07 at the top of the cupportion.

The interior surface of the cup portion is stepped to insure accuratespacing between perforated discs or baflie plates I08 and I09 and toprovide chambers of definite areas on opposite sides of these plates.The anode structure is held within the insulating cylinder by a lockingscrew, .not shown. A voltage is supplied to the anode structure by aleading-in wire IIO which is sealed in the side of the stem 92 andconnected to the upright support I03, the support carrying a short stubwire I II which is attached to the edge of the anode structure. Anelongated focussing electrode H2 is provided at its lower end with areinforcing collar which is threaded to receive screws which passthrough the cylindrical insulator I05 to hold it rigidly in position. Itwill be noted from this assembly that the cathode is completely enclosedby the shield electrode 98 and this electrode is reentrant with respectto the cup portion of the anode structure and the anode to! is reentrantwith respect to the focussing electrode M2.

A second electrode unit is supported from the stem 90 by a structureincluding clamping bands II t, II5 which embrace the stem and carrysupport rods H5 and Iii. These rods are attached to an insulating discH8 having a central hole in Y which is situated a metallic cylinder M9.The

metallic cylinder I I9 is held on the disc M8 by a flanged rim I2t andis concentric with and partially surrounds the end of the elongatedfocussing member 2. A pair of rods I2I and I22 project upwardly from thedisc H8 and carry a pair of parallel plates, only one of which is shownat I23. A similar pair of rods, I24 and I25, of longer length, extendfrom the disc 8 and 'carry a pair of parallel plates I26 and I21 whichare arranged at right angles to the plane of the plate I23. A graphitecoating I28 is formed on the wall of the tube from a point I29 up to thescreen I6 and an electrical connection is made with thiscoating by aleading-in wire I30 sealed in an arm NH. The voltage applied to themetallic coating on the wall of the vessel is also applied "to thecylindrical metallic electrode H9 by a helical expansion spring I32which presses against the metallic coating on the wall of the vessel andis attached to a conductor I33 which passes through the insulating discand is attached to the side wall of the cylindrical electrode H9. Thefour deflecting plates are provided with suitable terminal wires whichare sealed in the top of thestem 90 and pass out of the vessel betweenthe cylindrical portion I and the long electric fleld produced in thevicinity of the cylindrical electrode H9 and the top ot the 0- cussingelectrode II2 forms a iocussing lens for- 1. A cathode ray dischargedevice comprising a highly evacuated vessel having a fluorescent screenat one end thereof, an electron emitter at the otherend thereof, aternary electron optical lens system between said emitter and saidscreen, and a non-metallic conductive coating on said vessel betweensaid lens system and said screen.

2. A cathode ray discharge device comprising a highly evacuated vesselhaving a fluorescent screen at one end thereof, an electron emitter atthe other end thereof, a ternary electron optical lens system betweensaid emitter and said screen, and a colloidal graphite layer on the wallof said vessel, said layer being uniform and continuous from said screento said lens system.

3. A cathode'ray discharge device comprising a highly evacuated vesselhaving a stem at one end, a fluorescent screen at the other end, anelectron emitter supported on said stem, a shield surrounding saidemitter and having an apertured closure at one end, an invertedcup-shaped member superimposed on said shield, a tubular anodeprojecting from the axis of said member, spaced parallel bafiie memberssituated in said member and having apertures in alignment with saidanode, and an elongated electrostatic tubular member adjacent saidanode.

4. A cathode ray discharge device comprising a highly evacuated vesselhaving a stem at one end and a screen at the other end, a conductivecoat ing on the wall of said vessel, an electron emitter supported bysaid stem, a primary iocussing member, a secondary focussing member, andan elongated focussing member, each of said members and said coatingsuccessively surrounding a beam of rays to be projected from saidemitter to said screen.

5. A cathode ray discharge device comprising a highly evacuated vesselhaving a stem, an electron emitter supported by said stem, a primaryfocussing member, a secondary focussing member, an elongated focussingmember, said members successively overlapping the adjacent boundary ofthe preceding member, and a graphite fllm on the wall of said vesselhaving a portion overlapping said elongated focussing member.

6. A cathode ray device comprising a highly evacuated vessel having afluorescent screen at one end, a cathode at the other end for projectinga beam of rays toward said screen, and a series of electrostaticfocussing members intermediate said screen and cathode and arranged toeliminate dispersion of said rays to the wall of said vessel throughoutthe length of said vessel, said members including a primary focussingmember, an electron trapping member, an anode, a distortion correctingmember, and a terminating member, said primary member, anode andcorrecting member each having a portion extending within the boundary ofthe succeeding member.

7. A cathode ray device comprising a highly portion, an outwardlytapered portion and a terminating wall portion, a fluorescent screen onsaid terminating wall portion, a non-metallic coating on said taperedportion, and a unitary electrode assembly on said stem supported withinsaid cylindrical portion, said electrode assembly including a cathode, acupshaped shield member surrounding said cathode, a cup-shaped electrontrapping member superimposed on said shield member, a tubular anodesupported by said trapping member in alignment with said cathode, and anelongated iocussing member surrounding a portion of said anode andcoaxially related therewith.

8. A cathode ray discharge device comprising a highly evacuated vesselhaving a fluorescent evacuated vessel having a stem, a cylindricalscreen at one end and a stem at the other end, and a unitary electrodestructure supported by said stem, said structure comprising an electronemitter, a shield having an aperture surrounding said emitter, acup-shaped member partially surrounding said shield and supported fromsaid stem, a tubular anode supported by, said member, an elongatedtubular focussing member insulatingly supported by said cup-shapedmember and partially surrounding said anode, a cylindrical metallicmember insulatingly supported by said tubular focussing member, aninsulator attached to said cylindrical member, and a plurality ofdeflecting plates carried by said insu- I

